Removing polygon grid from displacement map?
In this case the grid effect on the map was caused by the amount of geometry on the low poly object. 

To remove the grid effect on a baked map (cycles/BI):


On the low poly object, Modifiers >> Add Modifier >> Subsurf >> use the default >> apply 
Create image for the map: UV Image Editor >> Create new (choose wanted size and rename), select the new image in the Node Editor so it is active
Select high poly, low poly, go to edit mode so uvs are visible
BI: Render >> Bake >> Bake Type: (choose map type, ex. Displacement), [x] Normalized, [x] Selected to active, [x] clear, Distance: (choose distance, ex. 0.18), Bias: (ex. 0.125, usually about 50-70% of the distance number), Margin: optional (default is ok) (should also work in cycles with cycles defaults)
Bake (without grid)! :D


If your object has less polys you may have to up the subsurf modifier to level 2 instead. My low poly had 1008 quads in this case and lv 1 worked to remove the grid. Also as a side note, in zbrush I started to have the grid appear again at higher poly counts (at the equivalent of a level 3 subsurf) for the low poly so it is kind of a test what poly count works best for the map problem. Usually about 4-5k poly is a good number to bake from to avoid the grid. 

Example of fixed Blender displacement map: